1. Field of the Invention
This invention relates to small motors, and particularly to small shaded-pole motors which are very thin in the direction of their output shafts.
2. Description of the Prior Art
Generally, with respect to machines and equipment used in the fields of electrical communications, business, instrumentation, etc., much effort is going into making a whole machine or equipment smaller, lighter, and less power consuming through the improvement of its parts with respect to materials used therefor and structures thereof. Hence, similar requirements are naturally also applied to electric motors used for such machines and equipment.
In prior art compact motors which have been used for the above applications, there are included shaded-pole motors having a shaft output of about 0.05-5 watts. A motor of this type has a stator core formed by laminating in general a number of stamped silicon steel sheets (high grade products use Fe-Co-V alloy sheets), stator coils wound on the core, and a rotor disposed within the hollow part of the stator. To maintain the amount of magnetic flux required for the gap portion in such a motor, the thickness of the stator core in the axial direction must be at least the same order as that of the rotor core. For this purpose, heretofore, silicon steel sheets or Fe-Co-V alloy sheets have been laminated to a thickness equal to that of the rotor core to form the stator core, which had the stator coils wound therearound. To provide the desired amount of flux, if the diameter of magnet wire used was 0.12 to 0.14 mm, the number of turns of the stator coil is required to be 1350-950 turns. Therefore, it has been said that, in the prior art shaded-pole motor, the thickness of the stator portion in the axial direction inevitably increased by the amount occupied by the stator coil relative to the axial thickness required for the rotor, so that the reduction of the thickness of the motor was difficult.
However, as whole machines and equipment are being made smaller, the motor itself is increasingly being required not only to be smaller, but also to have its thickness reduced.
Accordingly, it is an object of the present invention to reduce the thickness of the shaded-pole motor without degrading its performance.